a) Field of the Invention
The present invention relates to a novel thermoplastic resin composition which can be utilized as a material for producing molded articles by injection molding, extrusion molding or a like means.
b) Related Art
Generally, polyphenylene ethers are excellent in heat resistance, hot water resistance, dimension stability, and mechanical and electrical properties. On the other hand, they have disadvantages; for example, they show unsatisfactory moldability due to their high melt viscosity, poor chemical resistance, and low impact resistance.
Known methods for improving moldability by lowering the melt viscosity of polyphenylene ethers while maintaining their excellent properties include use of a mixture of a polyphenylene ether and a polystyrene resin. However, these known methods still fail to improve chemical resistance.
On the other hand, propylene polymers are not only excellent in various properties such as moldability, toughness, water resistance, chemical resistance, etc., but also they have low specific gravity and are cheap in cost; they have been widely used as a material for preparing various molded articles, films, sheets, etc.
However, the propylene polymers have defects or points which need to be improved in heat resistance, rigidity, impact resistance, coatability, adhesiveness, etc., which creates an obstacle in developing new practical utility. In particular, improvement in the heat resistance and impact resistance thereof is strongly desired.
Naturally, it may be expected to blend a polyphenylene ether and a propylene polymer to prepare a resin composition which could have the advantages of the both polymers and which could have improved moldability and impact resistance, and thus a wide possibility of new application would be available.
Blending a polyphenylene with a propylene polymer, however, actually gives rise to a resin composition in which miscibility of both polymers is poor so that molded articles obtained from such a blend as by injection molding, suffers phase separation between the polyphenylene ether and the propylene polymer, thereby providing articles having an extremely poor appearance and poor mechanical properties, which are unsatisfactory for practical purposes.
A method for improving the miscibility between a polyphenylene ether and a propylene polymer is known, as described in Published Japanese Patent Publication No. 22344/1981, in which method a polyphenylene ether is blended with a propylene polymer having bound thereon, a styrene based monomer by graft copolymerization. This method, however, fails to provide a composition having excellent impact resistance.
A resin composition having superior mechanical properties can be obtained by the incorporation of polyphenylene ether with a styrene monomer-grafted propylene polymer and a rubbery substance, as disclosed in Unexamined Japanese Patent Publication No. 207349/1989. However, conditions for dispersion phase of the components are not defined clearly.
Under these circumstances, there has been a strong demand for a composition composed of polyphenylene ether, modified propylene polymer, and rubbery substance, said composition having good mechanical properties and giving injection molded articles with a good appearance.
In view of the forgoing, the present inventors have studied intensively and extensively in order to develop effective technology, and as a result they have succeeded in the production of a new resin composition which is superior in heat resistance, melt-flow characteristic, processability, chemical resistance, appearance and gloss.